1. Field of the Invention
The present invention relates to a pouch type rechargeable battery. In particular, the present invention relates to a pouch type rechargeable battery that can emit gas that is generated therein when the rechargeable battery is overcharged or exposed to a high-temperature atmosphere and can also improve workability when installed in a battery pack.
2. Description of the Prior Art
Recently, as portable electronic devices have become increasingly compact and lightweight, the batteries that are used as power sources for these devices are being fabricated in compact sizes with high power storage capacity. For example, lithium ion rechargeable batteries have an operational voltage of more than 3.6 V, which is about three times that of Ni—Cd batteries or Ni—MH batteries that are used as power sources for portable electronic devices. In addition, the lithium ion rechargeable batteries have high energy density per unit weight so they are extensively used in the advanced electronic technology fields.
A lithium ion rechargeable battery generates electrical energy based on a set of oxidation-reduction reactions that occur at a positive electrode and a negative electrode. The lithium ion battery includes positive electrode active materials and negative electrode active materials that are capable of reversibly intercalating the lithium ions into or deintercalating the lithium ions from the positive electrode and negative electrode. The battery further includes an organic electrolyte or a polymer electrolyte that is filled between the positive electrode and the negative electrode.
The rechargeable batteries may be fabricated in various shapes and are classified according to external appearances of the cases that hold the electrode assemblies. For example, cylinder-type rechargeable batteries use cylindrical aluminum cans, square type rechargeable batteries use square type aluminum cans, and pouch type rechargeable batteries are housed in a laminated pouch case.
FIG. 1 is a perspective view that illustrates a conventional pouch type rechargeable battery.
Referring to FIG. 1, the conventional pouch type rechargeable battery includes an electrode assembly 10 and a pouch case 20 that receives and seals the electrode assembly 10. The electrode assembly 10 has a first electrode 12, a second electrode 14, and a separator 13 that is interposed between the first electrode 12 and second electrode 14. The components of the electrode assembly are stacked in the form of a stacked-type electrode assembly or wound in a jelly roll type electrode assembly. First electrode tab 15 and second electrode tab 16 extend from one side of an electrode plate of the electrode assembly 10, respectively, such that some parts of the first electrode tab 15 and second electrode tab 16 are exposed outside a pouch case 20. Protective tapes 17 are attached to the first electrode tab 15 and second electrode tab 16.
The pouch case 20 includes a case cover 22 and a case body 24 that have a space 25 for receiving the electrode assembly 10 therein. At least one side portion of the case body 24 is integrally connected with at least one side portion of the case cover 22. Remaining side portions of the case body 24 may form side sealing sections 24a and an upper sealing section 24b around the space 25 to receive the electrode assembly 10.
When the electrode assembly 10 is placed in the space 25 of the case body 24, the case body 24 makes contact with the case cover 22. The side sealing sections 24a and the upper sealing section 24b are thermally bonded to the case cover 22, thereby securely sealing the case body 24.
In order to reduce the volume of the pouch type rechargeable battery when it is accommodated in a battery pack, the side sealing sections 24a are folded toward both sides of the case body 24. As consumers may require round type portable electronic devices, the pouch type rechargeable battery must also be accommodated in a round type battery pack. At this time, edges of the side sealing sections 24a may scratch or dent the battery pack, thereby lowering the efficiency of a battery pack manufacturing process.
In addition, if a pouch type rechargeable battery is overcharged or exposed to a high-temperature atmosphere, the electrolyte may react with an active material layer of an electrode plate or the electrolyte. The active material layer may dissolve in the electrolyte, is thereby generating gas in the pouch case 20. Accordingly, the temperature and internal pressure of the pouch type rechargeable battery may rise, thereby causing a fire or an explosion of the pouch type rechargeable battery.